diff --git a/src/ProjectFileIO.cpp b/src/ProjectFileIO.cpp
index 36454a265..0c9fc32e9 100644
--- a/src/ProjectFileIO.cpp
+++ b/src/ProjectFileIO.cpp
@@ -1539,10 +1539,8 @@ bool ProjectFileIO::ImportProject(const FilePath &fileName)
    }
 
    wxString project;
-   BlockIDs blockids;
 
-   // Decode it while capturing the associated sample blockids
-   project = ProjectSerializer::Decode(buffer, blockids);
+   project = ProjectSerializer::Decode(buffer);
    if (project.size() == 0)
    {
       SetError(XO("Unable to decode project document"));
@@ -1788,7 +1786,6 @@ bool ProjectFileIO::LoadProject(const FilePath &fileName)
       return false;
    }
 
-   BlockIDs blockids;
    wxString project;
    wxMemoryBuffer buffer;
    bool usedAutosave = true;
@@ -1821,8 +1818,7 @@ bool ProjectFileIO::LoadProject(const FilePath &fileName)
    }
    else
    {
-      // Decode it while capturing the associated sample blockids
-      project = ProjectSerializer::Decode(buffer, blockids);
+      project = ProjectSerializer::Decode(buffer);
       if (project.empty())
       {
          SetError(XO("Unable to decode project document"));
@@ -1830,15 +1826,6 @@ bool ProjectFileIO::LoadProject(const FilePath &fileName)
          return false;
       }
 
-      // Check for orphans blocks...sets mRecovered if any were deleted
-      if (blockids.size() > 0)
-      {
-         if (!DeleteBlocks(blockids, true))
-         {
-            return false;
-         }
-      }
-
       XMLFileReader xmlFile;
 
       // Load 'er up
@@ -1852,6 +1839,19 @@ bool ProjectFileIO::LoadProject(const FilePath &fileName)
          return false;
       }
 
+      // Check for orphans blocks...sets mRecovered if any were deleted
+      
+      auto blockids = WaveTrackFactory::Get( mProject )
+         .GetSampleBlockFactory()
+            ->GetActiveBlockIDs();
+      if (blockids.size() > 0)
+      {
+         if (!DeleteBlocks(blockids, true))
+         {
+            return false;
+         }
+      }
+   
       // Remember if we used autosave or not
       if (usedAutosave)
       {
diff --git a/src/ProjectSerializer.cpp b/src/ProjectSerializer.cpp
index adfcec24c..6bb5025c5 100644
--- a/src/ProjectSerializer.cpp
+++ b/src/ProjectSerializer.cpp
@@ -383,7 +383,7 @@ bool ProjectSerializer::DictChanged() const
 }
 
 // See ProjectFileIO::LoadProject() for explanation of the blockids arg
-wxString ProjectSerializer::Decode(const wxMemoryBuffer &buffer, BlockIDs &blockids)
+wxString ProjectSerializer::Decode(const wxMemoryBuffer &buffer)
 {
    wxMemoryInputStream in(buffer.GetData(), buffer.GetDataLen());
 
@@ -549,16 +549,6 @@ wxString ProjectSerializer::Decode(const wxMemoryBuffer &buffer, BlockIDs &block
             {
                id = ReadUShort( in );
                long long val = ReadLongLong( in );
-
-               // Look for and save the "blockid" values to support orphan
-               // block checking. This should be removed once serialization
-               // and related blocks become part of the same transaction.
-               const wxString &name = Lookup(id);
-               if (name.IsSameAs(wxT("blockid")))
-               {
-                  blockids.insert(val);
-               }
-
                out.WriteAttr(Lookup(id), val);
             }
             break;
diff --git a/src/ProjectSerializer.h b/src/ProjectSerializer.h
index 5e561216f..1b023ea69 100644
--- a/src/ProjectSerializer.h
+++ b/src/ProjectSerializer.h
@@ -22,9 +22,6 @@
 // From SampleBlock.h
 using SampleBlockID = long long;
 
-// From ProjectFileiIO.h
-using BlockIDs = std::unordered_set<SampleBlockID>;
-
 ///
 /// ProjectSerializer
 ///
@@ -69,7 +66,7 @@ public:
    bool DictChanged() const;
 
    // Returns empty string if decoding fails
-   static wxString Decode(const wxMemoryBuffer &buffer, BlockIDs &blockids);
+   static wxString Decode(const wxMemoryBuffer &buffer);
 
 private:
    void WriteName(const wxString & name);
diff --git a/src/SampleBlock.h b/src/SampleBlock.h
index 0ff536609..a5bfc601c 100644
--- a/src/SampleBlock.h
+++ b/src/SampleBlock.h
@@ -13,6 +13,7 @@ SampleBlock.h
 
 #include <functional>
 #include <memory>
+#include <unordered_set>
 
 class AudacityProject;
 class ProjectFileIO;
@@ -133,6 +134,10 @@ public:
       sampleFormat srcformat,
       const wxChar **attrs);
 
+   using SampleBlockIDs = std::unordered_set<SampleBlockID>;
+   /*! @return ids of all sample blocks created by this factory and still extant */
+   virtual SampleBlockIDs GetActiveBlockIDs() = 0;
+
 protected:
    // The override should throw more informative exceptions on error than the
    // default InconsistencyException thrown by Create
diff --git a/src/SqliteSampleBlock.cpp b/src/SqliteSampleBlock.cpp
index 568ee5fb5..766759c6d 100644
--- a/src/SqliteSampleBlock.cpp
+++ b/src/SqliteSampleBlock.cpp
@@ -129,6 +129,8 @@ public:
 
    ~SqliteSampleBlockFactory() override;
 
+   SampleBlockIDs GetActiveBlockIDs() override;
+
    SampleBlockPtr DoGet(SampleBlockID sbid) override;
 
    SampleBlockPtr DoCreate(samplePtr src,
@@ -171,6 +173,21 @@ SampleBlockPtr SqliteSampleBlockFactory::DoCreate(
    return sb;
 }
 
+auto SqliteSampleBlockFactory::GetActiveBlockIDs() -> SampleBlockIDs
+{
+   SampleBlockIDs result;
+   for (auto end = mAllBlocks.end(), it = mAllBlocks.begin(); it != end;) {
+      if (it->second.expired())
+         // Tighten up the map
+         it = mAllBlocks.erase(it);
+      else {
+         result.insert( it->first );
+         ++it;
+      }
+   }
+   return result;
+}
+
 SampleBlockPtr SqliteSampleBlockFactory::DoCreateSilent(
    size_t numsamples, sampleFormat srcformat )
 {